Rotary seals, which include rotating members in sealable engagement with one another, are frequently used in various parts of gas turbine engines. The purpose of such rotary seals is to prevent fluid, such as air, in a gas turbine chamber at one pressure from passing to a chamber at a different pressure. Knife edge seal assemblies are one variety of rotary seal employed in gas turbine engines. Knife edge seal assemblies typically include a disk with an integral flange with one or more radial projections, known as “knife edges,” and a honeycomb ring seal attached to a guide vane. The disk and knife edge rotate with other components of the gas turbine, while the guide vane and honeycomb ring seal are stationary. The knife edge and honeycomb ring seal are assembled relative to each other to leave a small radial gap between the top of the knife edge and the inner surface of the honeycomb ring seal before the knife edge begins rotating in the gas turbine. Once the gas turbine begins operating, the centrifugal force created by the rotational speed of the gas turbine and the mass of the knife edge closes the gap between the knife edge and honeycomb ring seal and causes the knife edge to cut into and seal with the honeycomb ring seal.
Knife edges frequently develop defects or are otherwise worn during operation in a gas turbine. The operational wear on knife edges necessitates repairing the seal assembly at intervals during the lifetime of a typical gas turbine engine. The radial gap between the knife edge and honeycomb ring seal is critical to the effectiveness of the rotating seal. Maintaining this gap during repair cycles of knife edge seal assemblies, to some extent, defines the bounds of satisfactory methods of repair. The radial gap between the knife edge and honeycomb ring seal is a function of the radial height of the knife edge and the radial thickness of the honeycomb ring seal. Honeycomb ring seals are commonly purchased with standard dimensions and then machined to finished dimensions appropriate for their intended application. Therefore, maintaining the radial gap between the knife edge and honeycomb ring seal is primarily a function of manipulating the radial height of the knife edge. Prior methods of repairing knife edges typically include adding material to the top of the knife edge and then grinding the added material to a finished radial height. However, these methods of repair have two primary disadvantages. First, the step of adding material to the worn knife edges typically involves heating the knife edge material and thereby heating the material surrounding the knife edge, for example, by welding additional material onto the knife edge. In that case, there is a risk that the heating will create deleterious effects to the part on which the knife edges are located, for example by creating thermo-mechanical stresses in the part. The second disadvantage of prior methods is that the means of adding material to the knife edge is dependent on the knife edge material and this dependency can complicate the method significantly. For example, high strength metals, such as Nickel alloys, are very difficult to weld and therefore may preclude some methods of repair that require adding material to the knife edge.